Angiographic roadmapping is a technique commonly used for catheter navigation in endovascular procedures performed through a small puncture wound or incision often in the groin. Blockages in the arteries or veins can be treated with balloon angioplasty or the placement of stents, all through this small puncture wound.
Roadmapping consists of superimposing a live fluoroscopic image on a previously stored digitally subtracted angiogram. The digitally subtracted angiogram is generated by computer techniques which compare an x-ray image of a region of the body before and after a contrast agent has been injected intravenously into the body. Tissues and blood vessels on the first image are digitally subtracted from the second image, leaving a clear picture of the artery which can then be studied independently and in isolation from the rest of the body.
An angiographic roadmapping procedure typically consists of three phases. In the first phase, a user acquires fluoroscopic images of the region of the patient's anatomy in which an endovascular procedure will be performed. Once the x-ray has been regulated, the system switches to the second phase, in which the user injects a contrast medium into the patient's blood stream to build an opacified roadmap of the vessels using a digital subtraction technique as previously described. In the third phase, the opacified roadmap is combined with a live fluoroscopic image of the relevant region of the patient's anatomy to allow a physician guiding a catheter to see the vasculature during catheter positioning, thus eliminating the need for injecting further contrast medium.
One problem with this technique is that if the physician decides to move the patient table or x-ray detector, the roadmap will no longer be registered with the live fluoroscopic images. This can produce gross motion artifacts that make the resulting display unusable. As a result, the roadmapping procedure needs to be restarted, which results in additional time for the procedure, and often requires a new contrast injection for the patient.
Further, if the physician wishes to change the field of view of the x-ray detector during the roadmapping procedure, doing so may require the current mask to be discarded, and a new roadmap mask to be built. This too results in additional time for the physician to perform the procedure and, again, use of an additional contrast injection for the patient.
Thus, there is a need for an improved method for angiographic roadmapping that enables a physician greater flexibility in performing catheter-based procedures. Such a method should enable a physician to reposition a patient table and/or x-ray detector, or to modify the field of view of the x-ray detector during the roadmapping procedure without requiring a new roadmap mask to be constructed.